1. Field of the Invention
The present invention relates to a radio telephone system, and in particular to a power supply device for a radio telephone system which can carry out radio communication during power failure by supplying a battery power of a wireless handset to a main body during the power failure.
2. Description of the Background Art
As illustrated in FIG. 1, a conventional wire telephone system includes: a telephone call detector 10 detecting a phone call from the other party; a power switching unit 20 switching power supplied from a central office through a local loop (a) to the inside of the system; and a voice communication unit 30 receiving the power through the power switching unit 20, and performing the telephone communication.
The telephone call detector 10 includes: a ring signal detector 11 detecting a ring signal from an electric signal transmitted through a public switched telephone network (PSTN) 1; and a speaker 12 generating a certain sound according to the output from the ring signal detector 11.
The power switching unit 20 includes: a hook switch 21 hooked off when the user holds a handset; a bridge diode 22 rectifying the power inputted through the local loop (a); and a loop switch 23 turned on when the hook switch 21 is hooked off, for switching the power rectified in the bridge diode 22 to the voice communication unit 30.
The voice communication unit 30 includes: a voice signal processing unit 31 converting the electric signal transmitted through the PSTN 1 into a voice electric signal; a wire handset 32 converting the voice electric signal outputted from the voice signal processing unit 31 into a voice signal; a keypad 33 inputting a telephone number of the other party; and a dialer 34 transmitting an electric signal corresponding to the telephone number inputted from the keypad 33.
The operation of the conventional wire telephone system will now be described in detail with reference to FIG. 1.
In general, a plurality of wire telephone systems are connected to the PSTN. Each of the plurality of wire telephone systems is provided with the power required for the telephone communication from the central office (not shown) through the local loop.
Accordingly, in the wire telephone system as shown in FIG. 1, when the user hooks off the wire handset 32 from the hook switch 21 for the telephone communication, a power switch SW2 is turned on. As a result, the power inputted through the local loop (a) and rectified in the bridge diode 22 is supplied to the voice communication unit 30 through the loop switch 23, and therefore the voice communication unit 30 performs the telephone communication by utilizing the inputted power.
That is, when the ring signal is inputted through the PSTN 1, the ring signal detector 11 of the telephone call detector 10 detects the ring signal from the electric signal, and outputs it to the speaker 12. Accordingly, the user recognizes by a bell that he has a telephone call.
Thereafter, when the user hooks off the wire handset 32 so as to answer the telephone call, the power is supplied to the voice communication unit 31 through the loop switch 23. Thus, the electric signal transmitted through the PSTN 1 is converted into the voice electric signal in the voice signal processing unit 31, and outputted to the wire handset 32. Accordingly, the user can perform the voice communication with the other party through the wire handset 32.
In addition, in the case that the user hooks off the wire handset 32 in order to make a telephone call, the power is also supplied to the voice communication unit 31 through the power switch 23. When the user inputs a telephone number of the other party through the keypad 33, the inputted telephone number is converted into an electric signal in the dialer 34, and outputted to the PSTN 1 through the local loop (a).
Accordingly, when the other party hooks off the wire handset, the user performs the voice communication through the wire handset 32. Here, the wire handset 32 converts the voice signal of the user into the voice electric signal, and the voice signal processing unit 31 converts the voice electric signal outputted from the wire handset 32 into the electric signal, and outputs it to the PSTN 1.
As discussed earlier, the conventional wire telephone system performs the voice communication by using the power supplied from the central office. Even if the power failure is generated in a place where the wire telephone is located, since the wire telephone system is normally operated, the wanted telephone communication can be always performed.
On the other hand, as the radio communication techniques have been developed, the radio telephone system using the wireless handset instead of the wire handset has been widely distributed and used in the PSTN. The radio telephone system includes: a main body which is a subscriber terminal of the PSTN; and a wireless handset performing the radio communication with the main body. If necessary, the wireless handset is provided in a multiple number.
Accordingly, the user carries out the low output and high frequency radio communication with the main body of the radio telephone system by employing the wireless handset. The main body performs the communication by connecting a signal transmitted from the wireless handset to the PSTN.
However, the radio telephone system requires a specific power in order to perform the communication between the wireless handset and the main body. Accordingly, in the conventional radio telephone system, in case the power is not supplied to the main body due to the power failure or the like, the communication between the main body and the wireless handset is impossible, and thus the radio communication cannot be carried out.